1. Field of the Invention
The present invention relates to a semiconductor device suitable for a circuit which is operated at a high speed, such as a logic device, and to a fabricating method of such a semiconductor device, and more particularly, to a semiconductor device having excellent electro-migration resistant ability and to a fabricating method of such a semiconductor device.
2 . Description of Related Art
In a semiconductor device, a density of current flowing through a wiring is increased due to a downsizing tendency of recent design rule and with this fact, a problem that reliability is lowered, which is called electro-migration, comes to the surface. In the electro-migration, Al atoms flow in the same direction as electrons, and after the Al atoms flow out, a void is formed in a place where Al atoms can not be supplied, and a wiring break and the like are caused.
Thereupon, a method for enhancing the reliability is employed by adding trace Cu to Al which is material of the wiring, or by forming a film made of TiN and Ti under the Al wiring as a barrier metal film.
However, even when Cu is added to Al, sufficient effect can not be obtained. When the barrier metal film made of TiN and Ti is formed, since the barrier metal film is also formed on a bottom of a via, the TiN film inhibits the flow of Al atoms reversely. Therefore, a void is formed in the via, the wiring is broken, and large-scale integrated circuit (LSI) and the like are not operated.
Thereupon, a method for forming only a Ti film as the barrier metal film under an upper layer wiring made of Al alloy is disclosed in Japanese Patent Application Laid-open No. 5-326512, Japanese Patent Application Laid-open No. 8-111455and Japanese Patent Application Laid-open No. 10-199973. According to this method, since no TiN film exists in the barrier metal film, Al atoms can move between the upper layer wiring and the lower layer wiring, and the electro-migration is suppressed.
However, in the fabricating method of a semiconductor device described in those publications, although the electro-migration in a via can be suppressed, there is a problem that electro-migration in the upper layer wiring can not be suppressed sufficiently.
It is an object of the present invention to provide a semiconductor device capable of sufficiently suppressing electro-migration in a via and an upper layer wiring, and a fabricating method of such a semiconductor device.
According to one aspect of the present invention, a semiconductor device comprises: a semiconductor substrate; a lower layer wiring formed on the semiconductor substrate; an interlayer insulating film formed on the lower layer wiring; a via hole formed in the interlayer insulating film and reaching the lower layer wiring; a barrier metal film embedded in a bottom of the via hole and made of refractory metal; a conductive film formed on the barrier metal film; and an upper layer wiring having a first Ti film, a TiN layer, a second Ti film and an Al or Al alloy film which are sequentially laminated on the interlayer insulating film. The upper layer wiring is connected to the conductive film.
In the present invention, since the barrier metal film comprises the metal film made of refractory metal, a problem with respect to the movement of Al atoms caused in the conventional semiconductor device in which a TiN film is formed does not exist. Therefore, the electro-migration resistant ability in a via is high. Further, in the upper layer wiring, since the first Ti film, the TiN layer and the second Ti film are formed under the Al or Al alloy film, the orientation property of the Al or Al alloy film is high, and a variation in crystal particle diameter is small in the wiring. Therefore, the electro-migration resistant ability in the upper layer wiring is high.
According to another aspect of the present invention, a fabricating method of a semiconductor device invention comprises a step of forming a lower layer wiring on a semiconductor substrate. Then, in this fabricating method, an interlayer insulating film is formed on the lower layer wiring. Next, a first Ti film is formed on the interlayer insulating film. Thereafter, a TiN film is formed on the first Ti film. Then, a via hole is formed in the TiN film, the first Ti film and the interlayer insulating film such as to reach the lower layer wiring. Then, a second Ti film and an Al or Al alloy film are sequentially formed in the via hole and on the TiN film. Next, a thermal treatment is carried out, thereby allowing Ti in the second Ti film and Al in the Al or Al alloy film to react with each other in a bottom of the via hole.
In the present invention, the via hole is formed after the first Ti film and the TiN film are formed on an interlayer insulating film and then, the second Ti film and the Al or Al alloy film are formed. Therefore, the TiN film is not formed in the via hole, and the electro-migration resistant ability in the via hole is high. Furthermore, in the upper layer wiring, since the orientation property of the Al or Al alloy film is high and a variation in crystal particle diameter is small as described above, the electro-migration resistant ability in the upper layer wiring is also high.